This invention relates to a low cost binder composition comprising a blend of a thermosetting spray dried phenolic resole resin and a phenolic crystalline compound having two or more hydroxyphenyl groups. The binder, among other uses, finds utility in the preparation of molding compounds.
Commercially, the phenolic powder molding industry is dominated by novolac powders. Thermosetting phenolic novolac molding powders are prepared in 5 distinct steps:
(1). Reacting phenol with aqueous formaldehyde under strongly acidic conditions.
(2). Distilling the reaction mixture to remove excess phenol and water.
(3). Flaking the hot phenolic novolac melt on a cold flaker belt into a handleable solid.
(4). Grinding the resulting solid thermoplastic novolac flake into a powder.
(5). Blending the novolac powder with powdered hexamethylenetetramine (hexa) to make it thermoset.
Thermosetting, mainly compression molded articles, are then produced by compounding the novolac-hexa powders into a wide variety of fillers, e.g., friction compounds like barytes for automotive brake pads, abrasive compounds like alumina for grinding wheels, refractory aggregates like magnesia and graphite for refractory bricks, glass fibers and fillers for automotive engine intake manifolds, inert fillers like calcium carbonate for lamp cement pastes, and in many other matrixes for articles that require good modulus retention at elevated temperatures. Also, the excellent adhesive properties of novolac molding powders make them useful for compounding with glass and textile fibers for automotive acoustical insulation, wood fiber for automotive interior door panels, textile fibers for automotive interior package trays, and wood flour for toilet seat moldings, etc.
Novolac powders are particularly suitable for making thermoset molding compounds as they: are free flowing and easily blended with other fibrous, granular or powdered components, including hexa; are resistant to sintering; have excellent hot flow characteristics since the powder melts with good fluidity at mold temperature, and flows, to wet out the matrix and fill voids before it thermosets; can be molded with short cycles; have excellent heat resistance and dimensional stability; have a very low flame smoke rating; and are low in cost.
Novolac molding powders, however, do suffer from one significant problem, mainly, the liberation of odiferous hexa decomposition products, such as trimethylamine and ammonia, during the high temperature molding process. High odor is particularly objectionable in articles molded for automotive interior components.
It is an object of this invention to provide novel thermosetting adhesive compositions.
It is another object of the present invention to provide a novel molding powder that retains some or all of the advantages described above for the novolac-hexa powders while producing molded articles that do not contain objectionable odors.
These objects are achieved by using a blend of a spray dried resole resin with a phenolic crystalline compound having two or more hydroxyphenyl groups.
Phenolic resole resins are prepared with an excess of formaldehyde and are therefore thermosetting and, unlike thermoplastic novolacs which are prepared with an excess of phenol, do not require compounding with hexamethylenetetramine (hexa, a formaldehyde source) to become thermosetting. The thermosetting, temperature sensitive nature of phenolic resoles, however, makes them much more difficult to prepare in solid form versus phenolic novolacs. Converting the resole to solid form requires significant heat input to remove the large amounts of water added from the aqueous formaldehyde used to make the resole. Too much temperature exposure may advance the resole to a state that renders it useless as a molding powder.
The fundamentally simpler and less expensive nature of phenolic resoles, often described as xe2x80x9cone stepxe2x80x9d or xe2x80x9cone stagexe2x80x9d resins versus the xe2x80x9ctwo stepxe2x80x9d or xe2x80x9ctwo stagexe2x80x9d (compounding with hexamine) novolacs, however, has fostered the description, in the prior art, of many different minimal heat input drying techniques for the preparation of solid phenolic resole resin molding powders, including:
(1). U.S. Pat. No. 5,047,275 of September 1991; U.S. Pat. No. 4,950,433 of August 1990 and U.S. Pat. No. 5,019,618 of May, 1981, all by S. Chiu which describe improving spray dryability of a low advanced phenol-formaldehyde resin by inclusion of a water soluble boron oxo compound.
(2). U.S. Pat. No. 4,708,967 of November 1987 by Ferentchak, et al. describes a centrifugal atomizer having a porous sintered metal filter ring, producing hollow resin particles.
(3). U.S. Pat. No. 4,626,569 of December 1986 by Waitkus, et al. example XXa, describes the solid pan cooling method, where substantially all of the water is removed by distillation and the hot, approx. 90 E C., molten thermosetting composition is discharged very quickly from the reaction vessel into thin layers in cooling pans where it cools rapidly forming a grindable solid, while retaining enough hot flow character to function as a molding powder.
(4). U.S. Pat. No. 4,542,204 of September 1985 by Shibahara, et al. describes dispersing the hot condensate in cold water with mechanical dewatering.
(5). U.S. Pat. No. 4,424,300 of January 1984 by O. Udvary, et al. describes spray drying by the spinning disc atomization process.
(6). U.S. Pat. No. 4,419,477 of December 1983 by Saeki, et al. in preparation example 2 describes a solid resole resin prepared by dehydration with distillation and rapid solid pan cooling.
(7). U.S. Pat. No. 4,414,378 of November 1983 by Koyama, et al. describes a reaction in dilute aqueous solution where a solid, reactive and fusible resole resin particle forms directly from a phenol formaldehyde reaction catalyzed with hydrochloric acid.
(8). U.S. Pat. No. 4,317,901 of March 1982 by H. Cosway, describes additions of polyvalent cationic precipitants with mechanical dewatering.
(9). U.S. Pat. No. 4,206,095 of July 1980 by J. Wynstra, et al. describes an aqueous suspension of a particulate resole with mechanical dewatering.
(10). U.S. Pat. No. 4,182,696 of January 1980 by Wynstra, et al. describes a precipitation and mechanical dewatering process.
(11). U.S. Pat. No. 4,098,770 of July 1978 by Berchem et al. describes a spray drying process.
Of the above methods only the spray drying techniques, such as described by Berchem, et al., Udvardy, et al., Ferentchak, et al., and S. Chiu, set forth hereinabove, all of which are incorporated herein by reference in their entirety, have reasonable economics and have gained significant commercial importance such as for use as adhesives in wood composite boards.
Thermosetting spray dried resoles, however, while having enough flow to function well as adhesives, do not have sufficient hot flow to function as molding powders, also referred herein simply as binders. Additionally, the spray dried resoles cause sticking in the molding equipment which, among other shortcomings, interferes with the flow of the molten binder. Resoles formulated to have better flow characteristics, such as those prepared by the method of Waitkus, may form sticky agglomerated masses in the hot air conveyance equipment and may sinter after cooling to a solid mass over a short period of time in their storable container due to inadequate moisture removal. The solid pan cooling method described by Waitkus while having the capability to produce material with acceptable hot flow has poor economics, as batch sizes must be kept small due to the requirement for very rapid discharge of the hot, molten thermosetting resole from the reaction vessel.
Several inventors have reported on improving the hot flow properties of solid phenolic resoles prepared via the solid pan cooling method by admixing the solid resole with phenolic novolac resins, including:
(1). U.S. Pat. No. 4,426,484 of January 1984 by Saeki, et al. which describes mixing a solid resole with a resorcinol novolac solid resin to improve cure properties in a pulverizer, kneader or mixer.
(2). U.S. Pat. No. 4,419,477 of December 1983 by Saeki, et al. which describes a mixture of a solid resole with solid novolac with addition of an aromatic carboxylic acid to improve cure properties.
(3). U.S. Pat. No. 4,157,993 of June 1979 by Funabiki, et al. which describes addition of a lubricant to a higher F:P (formaldehyde to phenol) mole ratio solid resole to inhibit xe2x80x9cblockingxe2x80x9d (sintering) prior to mixing with the solid novolac.
U.S. Pat. No. 4,626,569, which is listed above describes adding a furfuraldehyde novolac to the dispersed resole prior to dewatering. U.S. Pat. No. 4,424,300 listed above, combines a liquid novolac with a liquid resole prior to spray drying.
Very little prior art exists on improving the hot flow properties of spray dried resoles by modification before spray drying as virtually anything that might be done to improve hot flow interferes with spray drying. The Chiu patents such as U.S. Pat. No. 5,047,275 listed above, produce a lower molecular weight resole, that would have better hot flow, if not for the boron oxo compound added to maintain spray dryability.
Additionally very little prior art exists on improving the hot flow properties of spray dried resoles by admixing other modifiers in the resoles prior to being spray dried.
The use of crystalline phenolic compounds such as bisphenol-A alone are not suitable as molding powders since they have a thin, watery flow and do not cure. However, crystalline phenolic compounds have been reacted with formaldehyde to make resins which allegedly can be used in the molding, coating or adhesive arts. U.S. Pat. No. 4,116,921 of September 1978 to Olivo, et al. reacts formaldehyde with bisphenol-A to prepare a resole resin which can be used for making molded articles. Both U.S. Pat. No. 5,571,854 of November 1996 and U.S. Pat. No. 5,691,409 of November 1997 to Isheda et al. use crystalline phenolic compounds as part of a molding composition which is cured with hexa. U.S. Pat. No. 4,182,732 of January 1980 to J. Fry discloses a coating and adhesive composition of a phenolic resole resin that may be in powdered form which is prepared from bisphenol-A and formaldehyde. U.S. Pat. No. 5,369,806 of June 1997 to C. Johnson, et al. discloses compositions comprising bisphenol-aldehyde novolac resins, or a bisphenol homopolymer novolac used for coating propants. The composition may also include a phenolic resole resin.
In a general aspect this invention relates to thermosetting adhesives.
In one aspect, this invention relates to a binder composition comprising a blend of a thermosetting spray dried phenolic resole resin and a crystalline phenolic compound having two or more hydroxyphenyl groups.
In another aspect, this invention relates to a thermoset product prepared from a blend of a spray dried phenolic resole resin and a crystalline phenolic compound having two or more hydroxyphenyl groups.
In still another aspect, this invention relates to a molding compound comprising a filler and a blend of a crystalline phenolic compound having two or more hydroxyphenyl groups and a thermosetting spray dried phenolic resole resin.
In still a further aspect, this invention relates to a molded article comprising a filler bound under heat and pressure with a thermoset binder of a crystalline phenolic compound having two or more hydroxyphenyl groups and a thermosetting spray dried phenolic resole resin.
In another further aspect, this invention relates to a method for making a molded article by subjecting a mixture of a filler and a blend of a thermosetting spray dried phenolic resole resin with a crystalline phenolic compound having two or more hydroxyphenyl groups to heat and pressure in order to cure the binder.
In another aspect, this invention relates to a method for increasing the flow of a thermosetting spray dried phenolic resole resin by blending such resin with a crystalline phenolic compound having two or more hydroxyphenyl groups.
Advantages of this invention for use in molding include the following: (a) absence of odiferous hexamethylenetetramine (hexa) decomposition product during high temperature molding processes; (B) faster molding times and fast cure rates; (C) higher modulus; and (D) decreased incidence of blister formation, particularly for high temperature-short mold cycle times. Additionally, the advantages include: the preparation of a binder composition economically by simply blending the spray dry resole with the crystalline phenolic; a water absorption of the novel thermoset binder which is much the same as that produced by commercial molding powders, e.g., a 1:1 binder of spray dried resole resin and a crystalline phenolic compound used in this invention had a water absorption of 2.78% whereas a commercial molding powder used for high temperature molding applications, namely, SD 571 B of Borden Chemical, Inc. of Columbus, Ohio had a water absorption of 2.71%. SD 571 B is a commercial molding powder containing 89.5% of phenol-formaldehyde novolac resin and 10.5% of hexamethylenetetramine which is sold by Borden Chemical, Inc of Columbus; and obtaining of dynamic temperature ramp properties of viscosity changes over time for the binders at molding temperatures, e.g., 135xc2x0 C., which are very similar to conventional novolac-hexa binders used for molding, e.g., such as the above mentioned SD 571 commercial molding powder. The binder compositions of this invention cure fairy completely as determined by acetone extractables.